[en] Temperature dependences of the carrier lifetime and photoluminescence (PL) spectra in Hg_1_-_xCd_xTe (0.3 < x < 0.4) epilayers grown on Si substrates (HgCdTe-on-Si) and intended for fabrication of p"+-n photodiodes have been studied. It is shown that the as-grown material has a high concentration of recombination centres with energy 30 ÷ 40 meV, which reduces the lifetime. The post-growth annealings, both that converting the material to the p-type and that imitating the activation of an implanted impurity, reduce the concentration of the centres. This manifests itself in an increase in the lifetime, which is especially noticeable after ’activating’ annealing and is confirmed by results of the PL studies. (paper)